This invention relates generally to the field of electrical insulation. The invention relates more particularly to the field of composite electrical insulation for use between the layers of copper that form the windings of an electrical generator rotor.
Electrical power generators are known in the art to contain rotor windings that are constructed of layers of copper rotor conductors. Multiple layers of copper are stacked radially in channels formed on the generator rotor. Layers of insulating material are installed between the individual layers of copper to provide both electrical insulation and a slip surface for accommodating differential movement between adjacent copper winding layers. The stack of copper and insulating layers is pre-loaded and mechanically constrained by a wedge device to minimize the movement of the layers and to restrain the stack as it undergoes centrifugal and electromagnetic forces during the operation of the generator.
A prior art insulating material for this application is a step-laminated epoxy glass NEMA grade G-11 composite material formed from multiple layers of prepreg that are pressed together under high pressure and temperature to form a roll format laminated material. This material is known to provide adequate compression creep resistance during centrifugal force loading and a surface that does not cause abrasion of the adjacent copper layer during turning gear operation. However, in order to achieve the required tolerance for overall thickness of this prior art laminated material, it is necessary to sand one side surface of the material before its use in an electrical generator. Sanding provides the required thickness control while the unsanded side provides an acceptable coefficient of friction for contact with the adjacent copper layer. The sanded side of the material is then coated with adhesive and affixed to a first layer of copper while the unsanded side is allowed to slip against the adjoining layer of copper. Step laminating has slow process cycle times, and the sanding step adds further time and expense to the manufacturing process, thus making the prior art step-laminated epoxy glass composite product expensive. Further, the step laminating process requires expensive tooling, thereby limiting the number of suppliers willing to invest in the required production facilities.
Accordingly, it is an object of this invention to provide an electrical insulating material for insulating between the layers of copper windings of an electrical generator that provides performance characteristics similar to prior art insulating material but that is less expensive to manufacture than prior art insulating material. Further, it is an object of this invention to provide a method for manufacturing an electrical insulating material for insulating between the layers of copper windings of an electrical generator that uses standard, inexpensive processing equipment.
In order to achieve these and other objects of this invention, an insulating material according to one aspect of this invention includes an electrically insulating substrate and a contacting layer disposed on the substrate; wherein the contacting layer provides a surface having a predetermined coefficient of friction. A method of manufacturing an insulating material according to another aspect of this invention includes the steps of providing an electrically insulating substrate, and disposing a contacting layer having a predetermined coefficient of friction on the substrate.